Frutexites from microbial/metazoan bioconstructions of Recent and Pleistocene submarine caves (Sicily, Italy)

Frutexites-like structures were recorded in small bioconstructions from Recent and Pleistocene marine caves. Theskeletal/microbialite frameworks hosting Frutexites form in cryptic environments characterized by poor lightavailability and reduced water circulation leading to confinement, oligotrophic conditions and the developmentof typical cave communities. Biostalactites and biotic crusts develop in the more confined parts of the both Recentand Pleistocene caves. They are composed of skeletal organisms engulfed in fine micrite sediments deposited insitu via microbial metabolic activity. The Frutexites, composed of Iron and Manganese oxides, are confined tomicrocavities or microfractures of the bioconstructions. They grow from an original discontinuity surface intothe surrounding consolidated micritic sediments. A model based on the increase of the microporosity of micriticsediments due to the dissolution of the original material and precipitation of ferromanganesiferous compoundswas proposed. This process occurs during the syndepositional diagenetic stage due to the intrusion in thebioconstruction framework of acidic continental water rich in Iron and Manganese. Mesophilic Fe–Mn autotrophicand chemoheterotrophic bacteria flourish on the microcavities and induce the precipitation of Fe and Mnoxides